def is_prime(n):

    if n < 2:

        return False

    for i in range(2, int(n**0.5) + 1):

        if n % i == 0:

            return False

    return True



def find_largest_prime(num):

    if len(str(num)) != 4:

        return 0

    digits = [int(d) for d in str(num)]

    permutations = set()

    for i in range(4):

        for j in range(4):

            for k in range(4):

                for l in range(4):

                    if i != j and i != k and i != l and j != k and j != l and k != l:

                        permutations.add(digits[i] * 1000 + digits[j] * 100 + digits[k] * 10 + digits[l])

    largest_prime = 0

    for num in permutations:

        if is_prime(num) and num > largest_prime:

            largest_prime = num

    return largest_prime



num = int(input())

largest_prime = find_largest_prime(num)

print(largest_prime)